The present invention concerns an electromagnetic actuator.
Such a device is generally of known art for many actuation tasks, for example in conjunction with internal combustion engines, and is mass-produced. The applicant's German utility model 20 2009 010 495 shows such an electromagnetic actuator, presupposed to be of generic form, in which an elongated plunger as a plunger unit is part of a multi-part armature unit of radially symmetric design; the latter can in turn be driven relative to a stationary core unit, by applying current to a stationary coil unit, so as to move the plunger. The plunger unit in turn engages on its end face with an actuation partner, which in the example of embodiment is a groove effecting a camshaft adjustment in an internal combustion engine.
Such established devices, presupposed to be of a generic form, combine a high level of operational reliability and low wear with favourable electromagnetic and production properties, wherein in particular the latter make the technology of known art suitable for mass production. However in such devices it is necessary, at least partially, i.e. in some sections, to enclose the stationary core region up to the permanent magnet unit of the armature unit; in specific implementations of the technology in accordance with DE 20 2009 010 495 this has been implemented in terms of housing elements in the form of a yoke. In particular in the case of installation volumes where space is critical, such as, for example, in the vicinity of an internal combustion engine camshaft, such flux-conducting parts of the housing limit the minimum installation dimensions that can be achieved, and predetermine de facto a minimum separation distance, for example, between a multiplicity of actuators to be provided adjacent to one another. Accordingly a need exists for a housing structure that can be implemented in a compact form, particularly in the radial direction.
A further disadvantage of the generic technology cited, which is in need of improvement, consists in the fact that in a zero applied current, stop-limited state of the armature unit (typically with the plunger unit in the retracted state) the detention forces that hold the armature unit in the core region are limited. Accordingly there is no possibility (or only a very limited possibility) of providing a compression spring, or similar energy store, between the armature unit and the core unit, with which, for purposes of achieving high dynamic properties (corresponding, for example to a high initial acceleration of the armature unit) when current is applied, the armature unit can be driven out of its stop-limited, i.e. stationary, position. In this respect the holding forces in the stationary state determine the maximum spring force that can be utilised in this situation. Accordingly from this perspective it is desirable to increase the holding forces of the armature unit on the stationary core region (core unit), generated by a permanent magnetic agent, so that in this respect it is possible to enable a more effective spring-assisted movement of the armature.